It is well known that various vehicle noise and drive line failure problems are directly traceable to torsional excitations from the engine. For example, the drive line of a typical wheel hauling unit includes an engine, a drive shaft, a transmission, a differential and final drive gear arrangement, and driven wheels arranged in series. Such vehicle drive lines frequently exhibit conditions of resonance corresponding to a certain engine speed, wherein the torsionally irregular impulses from the engine have a frequency generally corresponding to the natural frequency of the mass elastic system. These resonant conditions have resulted in not only vexatious vehicle vibration and noise problems, but also in drive line failures after extended service of the vehicle.
A number of methods of vibration control have been commercially developed to reduce the severity of these engine excitation problems. One relatively common solution is to incorporate an elastomeric flexible coupling in series with the drive line for lowering the natural frequency of the system, and for otherwise absorbing engine torsional vibrations. While these flexible couplings to absorb some shock and can desirably accommodate shaft misalignment, they are not totally effective and are susceptible to fatigue failure. Such failures occur because the coupling must transmit full drive line torque and must be responsive to a relatively broad range of operating frequency.
More specifically, when the torsional natural frequency of the engine, transmission, and intermediate drive shaft is below approximately 30 hertz or particularly in the range of 9 to 13 hertz (cycles per second), the normally acceptable flexible coupling and vibration absorber solutions become entirely inadequate. Viscous engine dampers of the type shown in U.S. Pat. No. 3,234,817 issued Feb. 15, 1966 to S. O. Williamson and assigned to the assignee of the present invention are frequently used to reduce the peak amplitudes of torsional vibrations. While these viscous dampers have been found extremely satisfactory at relatively high natural frequency ranges, for example, from 140 to 220 hertz, they are generally unacceptable for solving relatively low frequency torsional drive line problems due to lack of sufficient relative velocity between the elements thereof which is a mandatory requirement for effective viscous damping.
Another apparent solution would appear to be use of a conventional engine vibration absorber of the type having an inertia mass radially outwardly secured to the engine crankshaft or the like through an intermediate elastomeric ring. Representative of this type of absorber is U.S. Pat. No. 3,314,304 issued Apr. 18, 1967 to R. H. Katzenberger which further discloses multiple inertia elements elastically connected in series. These radial arrangements are also unsatisfactory for solving low frequency drive line vibration problems because they cannot be made torsionally soft enough while simultaneously maintaining sufficient radial and axial stability of one or more of the inertia masses.
It should be appreciated also, that any vibration absorber that would solve the aforementioned relatively low natural frequency of vibration problems should also be economical in construction, easily adaptable and serviceable with respect to the vehicle drive line, and be capable of association with other vibration absorbers such as the viscous engine damper without an adverse affect thereon.